N-Hydroxylation is believed to be the common intermediate in the nephrotoxicity, hepatotoxicity, hemolysis, methemoglobinemia and carcinogenesis of N-arylacetamides. The hepatotoxicity of acetaminophen is believed to be mediated by a toxic metabolite produced by N-hydroxylation. N-hydroxylation of polycyclic N-arylacetamides followed by N-O-sulfation is believed to produce one of the ultimate carcinogenic metabolites of these compounds. Since we have shown that the analgesic phenacetin and related compounds are N-hydroxylated we have examined the capacity of these compounds to be sulfated and glucuronidated. These N-hydroxy compounds were shown to be readily sulfated and glucuronidated. Following sulfation of N-hydroxyphenacetin or N-hydroxy-2-acetylaminofluorene a relative metabolite was immediately formed and covalently bound to protein. Following glucuronidation of N-hydroxyphenacetin a reactive metabolite was formed, but at a slower rate, the one half life was 8.7 hours. An examination of breakdown products of purified N-hydroxyphenacetin glucuronide under varying conditions implicated acetylimidoquinone as the reactive metabolite. This metabolite could either covalently bind to protein, be reduces to acetaminophen or undergo hydrolysis to quinone and acetamide. BIBLIOGRAPHIC REFERENCE: Mulder, G.J., Hinson, J.A. and Gillette, J.R.: Generation of reactive metabolites of N-hydroxyphenacetin by glucuronidation and sulfation. Biochemical Pharmacology 26: 189-196,$ 1977.